The present invention relates to a positional device which will provide three electrical signals proportional to the movement of a portion of the device in three dimensional space, i.e. proportional to the three coordinate axes x, y and z defining that position, and particularly although not exclusively to a device for use in conjunction with a computer to enable the movement of a cursor or object in the x-y and z directions as represented on a computer monitor.
Conventional arrangements used with computers to locate the precise position of a cursor on a screen (as in the Xerox Corporation xe2x80x9cmousexe2x80x9d) are capable only of providing a signal relating to movement in two dimensions. It is known that existing mouse type positioning devices and also similar two dimensional positioning devices such as touch screens, light pens, etc. are often inaccurate, difficult to use, ergonomically tiring, often restrictive in use and particularly in the case of the mouse, prone to degradation through the accumulation of dust and dirt.
Existing positional devices for computers are known, where a signal relating to position is determined by the interaction of a Hall effect device with a magnetic field. Hall devices are a known method of determining magnetic field strength, they depend on the interaction of a magnetic field on the current carried in a conductive material, typically a thin layer of a semiconductor. We refer to the Hall effect, first discovered by E. H. Hall in 1878 and the technology subsequently refined since then.
The principal features of the Hall effect are that the incidence of a magnetic field (B-field) on a current carrying conductor yields a Hall voltage, proportional to B. This Hall voltage is a maximum when the B-field and conductor surface are orthogonal.
Now, any magnetic field exists in three dimensions and a system of Hall devices located near a point in magnetic space will give Hall voltages which are a unique function of that point in magnetic space. If a system of magnets are used to develop a particular spatial magnetic field configuration and this system is mobile, relative to a system of Hall probes, then the Hall voltages generated in these Hall devices will, after processing, define the position of the magnetic system.
A number of patent applications have utilised this approach, in particular the following:
U.S. Pat. No. 4,459,578 Jul. 10, 1984
U.S. Pat. No. 4,639,667 Jan. 21, 1987
U.S. Pat. No. 4,654,576 Mar. 31, 1987
U.S. Pat. No. 4,825,157 Apr. 25, 1989
A disadvantage with this approach is the looseness, ambiguity and lack of precision of the geometric centre of such a magnetic assembly. Other disadvantages are the smallness of the B-field, the difficulty of flux concentration and that the movement of magnets generates circulating currents in the magnetic material creating additional fields superimposed on the main ones. A practical disadvantage is that such a magnetic sensor is often large and very bulky. The use of large magnets may also necessitate the use of shielding to prevent the magnetic field generated from interfering with magnetically sensitive equipment.
Another existing arrangement is described in WO 93/20535. This arrangement takes the form of a joystick and comprises a body including an end wall in which is secured a resilient arm. The resilient arm has secured to its top a tube and a handle. The tube surrounds the arm and mounts an annular magnet at the level of a pivot point, about which the arm flexes. The outputs of four Hall effect probes are affected by the position of the magnet to give an indication of the position of the arm, in two dimensions. The angular position of a, second, rotary handle is sensed by way of a further magnet which is connected for movement with the handle relative to further Hall effect probes.
Another use of a Hall effect device is disclosed in U.S. Pat. No. 5,004,871 which describes a stylus of a type suitable for use with a computer. The stylus has a pressure sensitive switch which may comprise a magnet and a Hall effect device mounted for movement relative to each other.
There are also a number of existing three dimensional positional devices available, for use in conjunction with computers. These devices use a variety of methods for generating a signal which relates to movement in three dimensions, including the use of gyroscopic systems to determine the movement of a device in space, electro-optical systems and in one device the use of strain gauges to determine the movement of a portion of the device relative to the remainder of the device. Existing three dimensional positional devices are expensive and/or imprecise, awkward and tiring to use, and in some cases physical constraints limit the use of the device.
An object of the present invention is to provide a three dimensional positional device which is convenient, simple and accurate and will, when used as an input device for a computer, enhance the capabilities of existing and future software technology and allow the exploitation of new more powerful computers.
Additional devices are foreseen for use with computer games, medical, computer graphics, virtual reality, robotics, security, teaching and other consumer and industrial applications.
According to a first aspect of the present invention there is provided a three dimensional positioning device comprising three Hall effect devices mounted on movable supports and three associated means for producing a magnetic field mounted on stationary supports adjacent but displaced from the movable supports.
Preferably the three magnetic systems are unconnected and unrelated. The magnetic systems each preferably comprise two magnets arranged in repelling mode polarity and the Hall effect devices are arranged to move between the opposed magnets. In this arrangement the Hall voltage measured will correspond to the position of the device between the two magnets, being a positive maximum when the Hall device is adjacent to one of the magnets and a negative maximum when the device is adjacent to the opposite magnet. The magnets preferably comprise small Nd.B.Fe Rare Earth magnets of high coercivity although they could comprise any other suitable magnetic material. The Hall devices are preferably comprised of conventional commercially available semiconductor Hall chips, although they could be effected by highly sensitive two dimensional electron gas (2DEG) Hall devices.
The three Hall devices and associated magnets are preferably mounted in a body having the appearance of the familiar two dimensional positional device, the mouse, but arranged to furnish three dimensional movement achieved by movement of the cover of the device with respect to its base. Movement of the three Hall devices may be proportional to the components of the movement of the cover of the device with respect to its base in three orthogonal directions. Springs may be employed to return the Hall devices to predetermined positions relative to their associated magnets when no external forces are applied to the device. Preferably the distance between any of the three positional modules (each comprising two opposed magnets and an associated Hall device) is greater than the distance between the opposed magnets of any one of the modules, more preferably the distance between any of the modules is at least twice the distance between the opposed magnets of any one module. The Hall voltages are preferably measured using conventional commercially available electronics and encoded for onward transmission to a computer by wire or by infra red or radio transmission, in which case the power supply for the device is preferably provided by means of a rechargeable battery and means for recharging this battery is provided integrally with the equipment that the positional device is intended for use with. The encoded information relating to the three Hall voltages is preferably processed by means of driver software which serves to move a cursor or object on the computer monitor in response to the signals received from the positional device, for example movement in two dimensions can be represented by movement of an object across the surface of a two dimensional screen and movement in a third dimension by changing the size of that object, although there are other possible ways that movement in three dimensions can be represented. The way in which the object controlled by the mouse behaves in response to movement of the positional device is also governed by its driver software and can be tailored to suit the application for which the positional device is to be used. Preferably movement of the cover of the positional device in a direction, for example sliding the cover in the x direction, causes the object controlled by the device to accelerate in that direction on the computer monitor and returning the device to the original position, or releasing one""s grip on the device, causes the object to stop moving. Also, the cover of the mouse type device preferably incorporates buttons, similar to the conventional two dimensional mouse, to provide additional input to software and could also, for example, enable the device to be used for input of six degrees of freedom, i.e. movement along and rotation about three orthogonal axes.
It will be appreciated, however, that other embodiments are possible, for example where a system of Hall effect devices are arranged, with appropriate mechanical linkages, in different device bodies. Examples of other possible embodiments include a joystick, single handed device, two handed or multi-user device and also location and motion detectors for industrial use.
According to a second aspect of the present invention there is provided a three dimensional positional device comprising a stationary portion and a movable portion wherein movement in two dimensions is effected by moving the movable portion in a plane relative to the stationary portion and movement in a third dimension is effected by pivoting the movable portion relative to the stationary portion.
Preferably, the axis about which the movable portion may be pivoted is parallel to the plane. Preferably, where movement of the movable portion in the plane is resolved into two axes, possibly for onward transmission, then the axis about which the movable portion may be pivoted is parallel to one of the two axes in the plane. Where movement in the plane is resolved into orthogonal axes, say x and y axes, then the movable portion may preferably be pivoted about an axis parallel to one of those axes, say the x-axis.
Where movement of the movable portion is encoded for onward transmission to a computer, or other device, then it is preferable that movement of the movable portion in the plane represents movement in the x-y plane and pivoting of the movable portion represents movement in the z direction, orthogonal to the x-y plane.
Movement of the movable portion relative to the stationary portion is preferably measured by means of a magnetic system comprising a Hall device or devices and means for producing a magnetic field, although any other suitable means may be employed, for example switches or an optical system. The Hall device or devices are preferably mounted on a movable support or supports and the means for producing a magnetic field mounted on a stationary support or supports, adjacent but displaced from the movable support(s). The movable supports are preferably linked to the movable portion of the device. The means for producing the magnetic field preferably comprises a permanent magnet or magnets, for example small Ndxe2x80x94Bexe2x80x94Fe Rare Earth magnets.
Preferably there are provided three Hall effect devices, movable relative to three unconnected and unrelated magnetic systems, as hereinbefore described. Two of the magnetic systems are preferably arranged to measure movement of the movable portion in each of two orthogonal directions in the plane and the third magnetic system the extent to which the movable portion is pivoted relative to the stationary portion.
In one embodiment two of the three Hall effect devices are mounted on slides, so arranged within the body of the positional device so that movement of the cover with respect to the base of the device results in the movement of the Hall devices relative to their associated magnets.
The remaining Hall device is preferably mounted on a pivoting member, arranged to move with the movable portion of the device, and its associated magnets are mounted on the stationary member. The slides may be connected directly to the movable portion, or by way of a connecting rod and pivot arrangement. A bearing or bearings may be disposed between the movable and stationary positions, to facilitate their relative movement. A resilient means, for example return springs may be disposed between the movable and stationary portions, to return the two portions to a predetermined relative position when no external force is applied.
The device preferably has the appearance of a conventional xe2x80x98mousexe2x80x99 device, the movable portion being comprised in the cover and the stationary portion being comprised in the base. The device may be arranged so that the movable portion may be pivoted about more than one axis, to allow for the input of additional degrees of freedom.
The present invention affords a number of advantages over the prior art, the use of static magnets eliminates the generation of eddy currents in nearby metallic members and hence additional magnetic fields generated by those currents and consequent errors in signals produced by the device. The use of a magnetic system is advantageous over those prior art devices which employ mechanical means for determining position, as magnet systems do not involve moving contacts they are unaffected by the accumulation of dust and dirt.
A means to exclude dust and dirt, for example a flexible skirt, may be disposed between the movable and stationary parts of the positional device.
Where a device may be used to provide two dimensional movement through sliding of a portion relative to another, and movement in a third dimension by pivoting, this provides a less ergonomically tiring arrangement than many prior art devices. The user may rest their hand on the device in use rather than having to raise or lower a portion of the device involving lifting their hand and arm. The provision of return to zero springs and more particularly variable rate return to zero springs can improve the feel of the device. Alternatively an actuator or actuators could be employed by counter movement of the device to give additional feed back to the user.
Referring, in particular, to the mouse type configuration, in use this embodiment is static relative to its surroundings in contrast to existing xe2x80x9cmousexe2x80x9d positioning devices which are mobile, this reduces the incidence of repetitive strain injury resulting from use of the device.
The use of three similar positional modules within the device results in a system which is easy and cheap to assemble. The three positional modules are small relative to the body of the device, particularly the distance between the two opposed magnets of each module is less than the distance between the separate modules, this reduces magnetic interference between the three modules and also the generation of external magnetic fields, this eliminates the need for shielding to prevent interference with outside, magnetically sensitive equipment.